If you do a character count on a LARGE TEXT field, even though it may be NULL the count returns as 10. If there are characters in that field, the character count is 10 + length of the string. I would think this is a bug. I am facing the same problem. For the fields that are <256, the count returns fine.
try {$nameOfField|count_characters:true}
try {$nameOfField|count_characters:true}